docs: def ensure_alt_ids_in_nest_spec_are_ints(nest_spec, list_elements):
      """
      Ensures that the alternative id's in `nest_spec` are integers. Raises a
      helpful ValueError if they are not.
  
      Parameters
      ----------
      nest_spec : OrderedDict, or None, optional.
          Keys are strings that define the name of the nests. Values are lists of
          alternative ids, denoting which alternatives belong to which nests.
          Each alternative id must only be associated with a single nest!
          Default == None.
      list_elements : list of lists of ints.
          Each element should correspond to one of the alternatives identified as
          belonging to a nest.
  
      Returns
      -------
      None.
      """
      try:
          assert all([isinstance(x, int) for x in list_elements])
      except AssertionError:
          msg = "All elements of the nest_spec values should be integers"
          raise ValueError(msg)
  
      return None